Of expressive/onomatopoeic origin; compare Slovene hlipati, Old East Slavic хлꙑграти (xlygrati).
хла́пити impf (Latin spelling hlápiti)
1 Croatian spelling: others omit the infinitive suffix completely and bind the clitic.
2 For masculine nouns; a feminine or neuter agent would use the feminine and neuter gender forms of the active past participle and auxiliary verb, respectively.
3 Often replaced by the past perfect in colloquial speech, i.e. the auxiliary verb biti (“to be”) is routinely dropped.
4 Often replaced by the conditional I in colloquial speech, i.e. the auxiliary verb biti (“to be”) is routinely dropped.
*Note: The aorist and imperfect were not present in, or have nowadays fallen into disuse in, many dialects and therefore they are routinely replaced by the past perfect in both formal and colloquial speech.