Field-name pattern: X + 学 = "the study of X." 昆虫 (insects) + 学 (study) → entomology. Same pattern: 心理学 (psychology), 语言学 (linguistics), 生物学 (biology), 经济学 (economics). The matching person-noun is 昆虫学家 ("entomologist").
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昆 in 昆虫 originally meant "a multitude / swarm" - 昆虫 = "the swarming creatures." Compare with 鸟类学 (bird-study, ornithology) and 鱼类学 (fish-study, ichthyology) - same -学 suffix, different animal.
