'claimant' originates from Old French (or Anglo-Norman) derived from the verb 'clamer'/'claimer' and the agent/participle suffix '-ant', ultimately from Latin 'clamare' meaning 'to shout' or 'to call'.

'claimant' changed from Old French present-participle forms (e.g. 'clamant'/'claimant') used to denote one who calls or proclaims, then entered Middle English and eventually became the modern English noun 'claimant' meaning someone who makes a claim.

Initially it meant 'one who calls out' (literally), but over time it evolved into its current meaning of 'one who asserts a claim or demands something (often legally or formally)'.