椅 (yǐ) is a bound form (b.f.) meaning 'chair'. It cannot stand alone as a word; you must attach 子 to form 椅子 (yǐzi, chair), or combine with other morphemes like 轮 (lún) to make 轮椅 (lúnyǐ, wheelchair). Note: the standard pronunciation for this sense is yǐ (third tone), though the source lists yī (first tone), which corresponds to a rare tree sense.