TOEFL Vocabulary: Science — TOEFL Academic Vocabulary
Science Five high-utility words with the full apparatus: pronunciation, both definitions, natural + academic examples, collocations, family, mistakes — then a 10-question set quiz.
hypothesis /haɪˈpɑːθəsɪs/ noun C1
Meaning: An idea that explains something and can be tested by experiments.
Academic meaning: A proposed, testable explanation for an observed phenomenon, formulated before data collection.
Natural example: Her hypothesis was that plants grow faster with music playing.
Academic example: The researchers tested the hypothesis that sleep loss impairs memory consolidation.
Collocations: form a hypothesis · test a hypothesis · support a hypothesis
Synonyms: theory, assumption, proposition
Word family: hypotheses (plural noun) · hypothetical (adjective) · hypothetically (adverb) · hypothesize (verb)
⚠ Common mistake: The plural is hypotheses, not hypothesises; a hypothesis is not yet proven, unlike a conclusion.
Register: Formal academic; core science vocabulary · Usage: Use hypothesis for an untested explanation; once strongly supported, it may become a theory.
experiment /ɪkˈspɛrəmənt/ noun B1
Meaning: A scientific test done to learn something or prove an idea.
Academic meaning: A controlled procedure carried out to test a hypothesis and observe measurable outcomes.
Natural example: We did an experiment with plants in science class today.
Academic example: In the experiment, reaction times were measured under three lighting conditions.
Collocations: conduct an experiment · carry out an experiment · a controlled experiment
Synonyms: test, trial, investigation
Word family: experimental (adjective) · experimentally (adverb) · experiment (verb)
⚠ Common mistake: Use the verbs conduct or carry out with experiment, not “make an experiment.”
Register: Neutral; used in everyday and academic English · Usage: Experiment as a verb (to experiment with) is also common in research contexts.
observe /əbˈzɝːv/ verb B2
Meaning: To watch something carefully in order to learn about it.
Academic meaning: To monitor and record phenomena systematically as part of data collection.
Natural example: We sat quietly to observe the birds in the garden.
Academic example: Astronomers observe distant galaxies using infrared telescopes.
Collocations: observe behavior · be observed in · observe a pattern
Synonyms: watch, notice, monitor
Antonyms: ignore, overlook
Word family: observation (noun) · observer (noun) · observable (adjective)
⚠ Common mistake: Observe means watch carefully; do not confuse it with obey, as in “observe the rules” (a different, formal use).
Register: Neutral–formal; very common in scientific reporting · Usage: In methods sections, observe describes systematic watching and recording, not casual looking.
theory /ˈθɪri/ noun B2
Meaning: A set of ideas that explains why something happens.
Academic meaning: A coherent, evidence-based framework that explains a class of phenomena and generates predictions.
Natural example: In theory, the trip should take three hours, but traffic is bad.
Academic example: Darwin's theory of evolution explains the diversity of species through natural selection.
Collocations: a scientific theory · in theory · develop a theory
Synonyms: framework, model, doctrine
Word family: theoretical (adjective) · theoretically (adverb) · theorist (noun)
⚠ Common mistake: In science, a theory is strongly supported by evidence — it does not mean a weak guess.
Register: Neutral–academic; also common in everyday speech with a weaker meaning · Usage: Specify scientific theory in academic writing to avoid the everyday “just a theory” misunderstanding.
variable /ˈvɛriəbəl/ noun C1
Meaning: Something that can change or be different in a situation or experiment.
Academic meaning: Any factor that is measured, manipulated, or controlled in an investigation.
Natural example: The weather is one variable we cannot control on the trip.
Academic example: Temperature was the independent variable, while growth rate was the dependent variable.
Collocations: independent variable · dependent variable · control a variable
Synonyms: factor, element, parameter
Antonyms: constant
Word family: vary (verb) · varied (adjective) · variation (noun) · variably (adverb)
⚠ Common mistake: In an experiment, distinguish the independent variable (changed by the researcher) from the dependent variable (measured).
Register: Academic/technical; central to research methods · Usage: Also used as an adjective meaning changeable: variable weather, variable costs.