Literally 'fat-loving'. Applied to molecular entities (or parts of molecular entities) having a tendency to dissolve in fat-like (e.g. hydrocarbon) solvents.
See also: hydrophilic, hydrophobic interaction, lyophilic
Sources:
PAC, 1972, 31, 577. 'Manual of Symbols and Terminology for Physicochemical Quantities and Units, Appendix II: Definitions, Terminology and Symbols in Colloid and Surface Chemistry' on page 607 (https://doi.org/10.1351/pac197231040577)
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1136 (https://doi.org/10.1351/pac199466051077)