We report the discovery by the HATSouth network of HATS-18b: a (ProQuest: Formulae and/or non-USASCII text omitted) planet in a 0.8378 day orbit, around a solar analog star (mass 1.037 + or - 0.047 Mmiddot in circle and radius (ProQuest: Formulae and/or non-USASCII text omitted) Rmiddot in circle) V= 14.067 + or - 0.040 mag. The high planet mass, combined with its short orbital period, implies strong tidal coupling between the planetary orbit and the star. In fact, given its inferred age, HATS-18 shows evidence of significant tidal spin up, which together with WASP-19 (a very similar system) allows us to constrain the tidal quality factor for Sun-like stars to be in the range of 6.5 <, ~ log sub(10)(Q*/k sub(2)) <, ~ 7 even after allowing for extremely pessimistic model uncertainties. In addition, the HATS-18 system is among the best systems (and often the best system) for testing a multitude of star-planet interactions, be they gravitational, magnetic, or radiative, as well as planet formation and migration theories.