In this case, 히 is used to produce an adverb. 완전히 = totally 간신히 = barely 솔직히 = frankly Other ones are 굉장히, 가뿐히...well these two are all I can think of right now.

let me know whole sentence. it uses depending upon the each situation.

히 can be used after verbs to create either causative or passive verbs. For example, the causative verb for 입다 (to wear) is 입히다 (to dress). Lesson on passive voice: http://www.talktomeinkorean.com/lessons/l6l21/ Lesson on making causative verbs: http://www.talktomeinkorean.com/lessons/l7l11/