Definitions

The American Heritage Dictionary of the English Language, Fourth Edition

pri·mo·gen·i·tor       Listen: [ prm-jn-tr ]
n.

1. The earliest ancestor.
2. An ancestor or forebear.

[Late Latin prmgenitor : Latin prm, at first (from prmus, first; see per¹ in Indo-European roots) + Latin genitor, begetter (from genitus, past participle of gignere, to beget; see gen- in Indo-European roots).]

The Random House Dictionary of The English Language - Second Edition unabridged

pri-mo-gen-i-tor (pri m jen i tr), n.

1. a first parent or earliest ancestor: Adam and Eve are the primogenitors of the human race.

2. a forefather or ancestor.

[1645-55; < LL prmgenitor ancestor. equiv. to L. prim at first + genitor GENITOR]

The Barnhardt Concise Dictionary of Etymology - The Origins of American Words - Robert K. Barnhardt 1988

primogenitor  n. 1654, borrowed possibly through French primogeniteur, and directly fom Late Latin prmogenitor (Latin prmus forst, + genitor begeter, from genit-, past participle stem of gignere beget); for suffix see -OR.

or  a suffix meaning person or thing that does (something) as in conqueror, donor, actor, accelerator

Not to be confused with primogeniture  n. 1602, borrowed probably through French primogeniture, and directly from Medieval Latin primogenitura, from Late Latin prmogenitus first born (Latin prmus first + genitus, past participle of gignere beget: see KIN); for suffix see -URE.

Webster's 1913 Dictionary

Pronunciation: `prImu'jenitur

Definition: [n] an ancestor in the direct line

Synonyms: progenitor

See Also: ancestor, antecedent, ascendant, ascendent, genitor, root

Definition: \Pri`mo*gen"i*tor\, n. [LL., fr. L. primus first + genitor a begetter.]
The first ancestor; a forefather.

\Pri`mo*gen"i*tor\, n. [LL., fr. L. primus first + genitor a begetter.] The first ancestor; a forefather.