烫 (tàng) covers anything where heat is pressed onto something - scalding water (烫水 tàngshuǐ), perming hair (烫发 tàngfà), or pressing clothes (烫衣). The 火 (fire) on the bottom is your hint.
grammar
Verb-object compound - split it for natural usage: 烫衣服 (tàng yīfu, iron the clothes), 烫一下衣服 (tàng yīxià yīfu, iron the clothes a bit), 烫了三件 (tàng le sān jiàn, ironed three pieces).
