'grievously' formed in Middle English by adding the adverbial suffix '-ly' to 'grievous'; 'grievous' originates from Old French (e.g. 'grevous' or 'grever') meaning 'to burden' or 'to oppress', ultimately traceable to Latin roots related to 'gravis' meaning 'heavy'.

Latin 'gravis' (meaning 'heavy') influenced verbs like Latin 'gravare' ('to make heavy, to burden'); this sense passed into Old French (verb 'grever', adjective forms 'grevous/grevous'), then into Middle English as 'grevous'/'grievous', and later the adverbial form 'grievously' was formed by adding '-ly' in English.

Initially related to physical weight or burden ('heavy' or 'burdensome'), the sense evolved to describe something that causes serious harm, sorrow, or offense; the adverb now commonly means 'in a severe or distressing way.'