Definitions

1. contraction

the past tense and second person singular and plural of ‘can’ or ‘could’, used to express possibility, ability, or permission

“I couldn’t find my phone anywhere.”

2. verb

used to express inability or impossibility, especially in the past

“She couldn’t speak English fluently when she was a child.”

3. auxiliary verb

used to form the past tense of another verb, typically in conjunction with ‘to have’ or ‘to be’

“He couldn’t have eaten so much food by himself.”