加(くわ)わるto be added to, to be appended, to join in (e.g. a group of friends), to participate, to increase (e.g. heat), to gain in (e.g. influence), to grow, to gather (speed), to be applied (e.g. heat, pressure), to be exerted

辞書の定義

「る」で終わる五段動詞, 自動詞
1.
to be added to, to be appended
「る」で終わる五段動詞, 自動詞
2.
to join in (e.g. a group of friends), to participate
「る」で終わる五段動詞, 自動詞
3.
to increase (e.g. heat), to gain in (e.g. influence), to grow, to gather (speed)
「る」で終わる五段動詞, 自動詞
4.
to be applied (e.g. heat, pressure), to be exerted