Lexical Definition

‎πρωτοστάτης‎ prōtostátēs (pro-tos-tat'-ace) ringleader ^G:N-M
from ‎πρῶτος‎ and ‎ἵστημι‎

ringleader.

• one standing first in the ranks, i.e. a captain (champion)

Abbott-Smith

πρωτοστάτης, -ου, ὁ (< πρῶτος, ἵστημι), [in LXX: Jb 15:24 AB*;]
prop., of soldiers, one who stands first, one in the front rank (Thuc., Xen.); hence, metaph., a leader: Ac 24:5.†

Abbott-Smith References

Liddell-Scott-Jones

πρωτοστάτης-στάτης [ᾰ], ου, ὁ,

(ἵστημι) one who stands first, especially the first man on the right of a line, right-hand man, ὁ π. τοῦ δεξιοῦ κέρως [Refs 5th c.BC+]; but also οἱ π. the front-rank men, [Refs 5th c.BC+]; either sense possible in [Refs 3rd c.BC+]

__2 ={λοχαγός}, [Refs 2nd c.AD+]
__3 man in the uneven rows in a λόχος, opposed to ἐπιστάτης, [Refs 1st c.BC+]
__II metaphorically, chief or leader of a party, [NT+3rd c.AD+]; π. τοῦ θητικοῦ καὶ οἰκετικοῦ[Refs 4th c.BC+]

_{LSJ Scripture Refs: Acts.24.5}