Although traditionally, a single line in a poem was called as verse, nowadays, this word is generally used to refer to the whole of the poem. So, more often, a poetical line is simply called as a line only (Please note that a line in verse is different from a sentence as it doesn’t necessarily follow grammatical rules). Rhythm, syllable-count, meter, etc. of a line in a poem are very important factors for critical appreciation, and even classification of poetry. A group of lines in a poem is known as a stanza.
Besides this, I have heard of a word called Stich (but not – stitch, which means to sew) that is used to refer to a single line of a poem or verse. But I don’t think this world has a common use.