Usage: 5 forms in 7 verses
Form Translated As     In Verse(s)
συνεπιτιθεμένων joining in attacking LXX.Ps.3.6
συνεπιτιθέμενα joining in making an attack LXX.Zech.1.15
συνεπιθώνται join in making an attack LXX.Deut.32.27
συνεπιθή join LXX.Num.12.11
joined in an attack LXX.Obad.1.13
συνεπέθεντο Agreed Acts.24.9
joined in making an attack LXX.Zech.1.15

Liddell-Scott-Jones

συνεπιτίθημι (sunepitithēmi) to join in making an attack TEGMC

συνεπιτίθημι-τίθημι,

help in putting on, put on still more, βάρος [Refs 1st c.AD+]

__II middle, join in attacking, τῷ Μήδῳ [NT+5th c.BC+]
__II.2 σ. τῷ ἔργῳ fall to the work together, [Refs 5th c.BC+]
__II.3 set upon and use to one's own advantage, σ. τῇ ἀγνοίᾳ, τῷ μίσει τινός, [Refs 2nd c.BC+]
__II.4 σ. τισὶ ἁμαρτίαν lay a sin to their charge, [LXX]

LSJ Scripture Refs: LXX.Deut.32.27Acts.24.9LXX.Num.12.11