Lexical Definition

‎συμπαθέω‎ sympathéō (soom-path-eh'-o) to sympathize ^G:V
from ‎συμπαθής‎

have compassion, be touched with a feeling of.

• to feel "sympathy" with, i.e. (by implication) to commiserate

Abbott-Smith

** συν-παθέω (Rec. συμπ-), -ῶ, [in LXX: IV Mac 5:25 AR 13:23 * ;]
to have a fellow feeling for or with, sympathize with or in: c. dat. rei, He 4:15; dat. pers., ib. 10:34 (Arist., Plut., al.).†

Abbott-Smith References

Liddell-Scott-Jones

συμπαθέω-έω,

to be sympathetically affected, δοκεῖ ἡ ψυχὴ καὶ τὸ σῶμα συμπαθέωεῖν ἀλλήλοις [Refs 4th c.BC+]:—passive, [Refs 1st c.AD+]

__2 with dative person, sympathize with, τοῖς φίλοις [Refs 4th c.BC+]
__3 with dative of things, sympathize in, feel for, ἀτυχίαις [NT+5th c.BC+]
__4 absolutely, feel sympathy, [Refs 1st c.AD+]; ἐκ τοῦ παθεῖν γίγνωσκε καὶ τὸ συμπαθέωεῖν· καὶ σοὶ γὰρ ἄλλος συμπαθέωήσεται παθών (future middle in active sense) [Refs 4th c.BC+]

_{LSJ Scripture Refs: Heb.4.15}