IPA: /ˌɪrɪˈprɛsəblɪ/
KK: /ɪrɪˈprɛsəblɪ/
In a way that cannot be controlled or held back; showing strong emotions or actions that are difficult to suppress.
She laughed irrepressibly at the funny joke, unable to contain her joy.
Irrepressibly → It is formed from "in-" (meaning not), "repress" (from Latin "reprimere", meaning to hold back or suppress), and "-ibly" (meaning in a manner). The word "irrepressibly" means in a manner that cannot be held back or suppressed.
Think of 'not' being able to 'hold back' something — that's why irrepressibly means something that cannot be contained.