To Grow Longer
To Be Stretched, To Make Progress
intransitive verb, ichidan verb
Because the hiragana ends with an う sound, you know this word is a verb. The kanji itself means stretch and the verb vocab version is to grow longer or to be stretched. You know that this is the version where you aren't doing the stretching, because you're letting someone stretch you on a torture rack in order to win a beer (びる). You're that desperate.
The reading is the one you learned with the kanji, you lucky duck!
この生地はよく伸びますね。
This material stretches well.
どうして彼女の英語力がグングン伸びてるのか知ってる？
Do you know why her English skills are rapidly improving?