Korean syllable 척

The Korean word around it decides its meaning. In -는 척하다, it presents an action or state as a performance: 아는 척 means acting as though you know. Repetition makes a different word: 척척 can describe a task going smoothly or people working in step.

Hangeul was designed to write Korean, with letters assembled into syllable blocks. A record of the script's creation dates to 1443; the explanatory book Hunminjeongeum was published in 1446 and describes its letters, sounds, and how they form blocks. 척 is one such block, made from ㅊ, ㅓ, and ㄱ.

Why can 아는 척 sound accusatory?

It can frame knowledge as an act someone is putting on. The National Institute of Korean Language distinguishes 아는 척하다 from 알은척하다: the first means pretending to know, while the second means acknowledging or greeting someone. If you mean the greeting, 알은척하다 is the relevant expression.

The repeated form 척척 follows a different pattern. In 척척 맞다, it describes people or things fitting or working in step, not pretending.

How do you type 척 as one Hangul block?

Type ㅊ, ㅓ, then final ㄱ on a Korean keyboard. A Korean input method assembles them into one syllable block. Text processing may also decompose 척 into these letters and recompose it during normalization, so the parts can appear separately even when the result displays as one block.

The same spelling appears in 배 한 척, where 척 counts a ship, and 이십오 척, where it names a traditional length unit. Those are distinct words; the neighboring noun or number tells you which one you have.