From Teflpedia

Buy (/baɪ/) is an English verb meaning "to obtain (something) in exchange for money or goods"[1]

"Buy" is an irregular verb. It has the 3rd person form "buys" (/baɪz/), the preterite and past participle "bought" (/bɔ:t/), and the -ing form "buying" (/baɪjɪŋ(g)/).

The antonym is buy is sell.

Buy is an transitive verb so (nearly always) needs a direct object. e.g. "I bought something". When used ditransitively, the person for whom the direct object is bought can be identified by using a for phrase, e.g. "I bought something for my wife". This can undergo dative shift, e.g. "I bought my wife something."

Buy can be used reflexively, e.g. "I bought something for myself", or "I bought myself something."

Students may try to use a to phrase instead of a for phrase, but we can't say *"I bought something to somebody." Students may also confuse "bought" with the similar sounding "brought" (see bring).