They swam in the pool all afternoon.

Meaning: They spent the entire afternoon swimming in the pool.

Choice of Words: Swam is the past tense of swim, which means to move through water using your arms and legs. In is used to indicate a location or position. Pool is a container filled with water for swimming or bathing. All means the entire amount or quantity. Afternoon is the time of day between noon and evening. When you put them together, the sentence means they were moving through the water using their arms and legs in the pool for the entire afternoon.

Alternative Expressions

Related Expressions