Greek expert, Dr. Spiros Zodhiates, was General Editor of The Complete Word Study Dictionary: New Testament. This quote is part of the article that defines the New Testament use of “spirit” as it relates to biblical psychology:

Spirit (Pneuma) B) rational spirit…element of life. 1) Generally, spirit distinct from the body and soul. See also Luke 1:47; Hebrews 4:12. Soul and spirit are very closely related because they are both immaterial and they both contrast with body (soma) and flesh (sarx). Scripture, however, introduces a distinction between the two immaterial aspects of man’s soul and spirit. They that they cannot mean the same thing is evident from their mention together in 1 Thess. 5:23: spirit, soul, body. The same distinction is brought out in Hebrews 4:12. The spirit is man’s immaterial nature which enables him to communicate with God, who is also spirit. 1 Corinthians 2:14 states that “the natural man receiveth not the things of the Spirit of God” because “they are spiritually discerned.” What is translated “natural man” in Greek is psuchikos, or … soulish, meaning the soul of man. The soul is the aspect of his immaterial nature that makes him aware of his body and his natural, physical environment. The difference between soul and spirit is not one of substance [both are the immaterial side]  but of operation.”

Thus, this reference book agrees with holistic trichotomy: man is one in personhood with two divisible parts (material and immaterial), yet three distinguishable parts (spirit, soul and body).

“Spirit”. The Complete Word Study Dictionary: New Testament. Gen Ed. Spiros Zodhiates with Dr. W. Baker, and Dr. G. Hadjiantoniou, (Chattanooga, AMG Publishers, 1993). Bracketed words added