Monosyllabic means answering in single short words and saying as little as possible. Yes. No. Fine. Whatever.
Strictly the word means having one syllable, and a linguist uses it that way about words themselves — cat and through are both monosyllabic. Everyday English has taken it somewhere better: a monosyllabic teenager is not being studied for phonology, they are being uncooperative. That second sense is now the commoner one by far, and it carries a flavour of sulking or exhaustion. The parts are worth knowing, since mono- means one and a syllable is a beat of sound.
1adjectivemonosyllabicReplying in very short words, saying as little as possible.
“He was monosyllabic all the way home.”
2adjectivesyllableOf a word, having only one syllable.
“The poem is built almost entirely from monosyllabic words.”
Latin
monosyllabicus
English, today
monosyllabic
Latin monosyllabicus, from Latin monosyllabus, from Hellenistic Ancient Greek μονοσύλλαβος. by surface analysis, monosyllable + -ic or mono- + syllabic.
Etymology from Wiktionary, CC BY-SA