Lexicon of Thomas Aquinas
vocātio, ōnis, f., a calling, vocation on the part of God. Est autem exsecutio praedestinationis vocatio et magnificatio, PP. Q. 23. Art. 2 c; vocatio semper est temporalis, quia ponit adductionem quandam ad aliquid, 1 Sent. 41. 1. 2 ad 3; vocatio importat distantiam in eo, qui vocatur, 4 Sent. 17. 1. 1. 2 ob. 3; vocatio est duplex quaedam exterior, ut quae fit per praedicatorem; et haec non est iustificatio, sed disponit ad eam. quaedam vero interior. et haec quandoque quidem non pertingit ad finem suum ex vocati defectu, et haec vocatio nihil aliud est, quam aliquis instinctus vel motus ad bonum a Deo immissus, et haec etiam vocatio non est idem, quod iustificatio, sed via ad illam. quandoque autem pertingit ad finem, quando scilicet aliquis audit vocantem et venit ad Christum …; et haec vocatio idem est, quod iustificatio, secundum substantiam, sed differt ratione, quia vocatio dicitur, secundum quod per infusionem gratiae et auxilium homo a peccato retrahitur, sed iustificatio respicit terminum ad quem, scilicet praedictae rectitudinis statum, 4 Sent. 17. 1. 1. 2 c. Cf. PP. Q. 23. Art. 8; PS. Q. 98. Art. 4; PS. Q. 113. Art. 1 (ter); Is. 1 b; Eph. 1. 4 and 4. 1; et passim.
Catholic Dictionary (1887):
vocation. In its more restricted and special sense vocation is taken for that “disposition of Divine Providence” whereby persons are invited to serve God in some special state—e.g. as ecclesiastics or religious. The ecclesiastical vocation is manifested by the pious desires of the heart, by innocence of life, by the sincere love of Christ, by pure zeal for God’s glory and the salvation of souls. That to the religious state, or the perfect practice of the evangelical counsels, comes to souls with a certain pressing invitation, with a strong desire of self-sacrifice and a clear perception of worldly vanity, with a certain attractiveness for intimacy with Christ and for the exaltation of his holy Name. But it is given differently to different persons, and prepares them “powerfully” though “sweetly” for the practice of solid virtue. “If thou wouldst be perfect,” said our Lord, “go sell what thou hast and give to the poor,.… and come, follow Me.”
ST II-IIae, q. 183
Yves Congar, Lay People in the Church, ch. 6, "Vocation"

Music attribution: "Bach - Brandenburg Concerto No 3, 3 allegro" by Advent Chamber Orchestra. Acquired here. Edited for length. Used under Attribution-Share Alike 3.0 United States License.