The Collaborative International Dictionary of English v.0.48:

Hirer \Hir"er\, n.
   One who hires. Hires

WordNet (r) 3.0 (2006):

hirer
    n 1: a person responsible for hiring workers; "the boss hired
         three more men for the new job" [syn: boss, hirer]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

HIRER, contracts. Called, in the civil law, conductor, and, in the French
law conducteur, procureur, locataire, is he who takes a thing from another,
to use it, and pays a compensation therefor. Wood's Inst. B. 3, c. 5, p.
236; Pothier, Louage, n. 1; Domat, B. 1, tit. 4, Sec. 1, n. 2; Jones' Bailm.
70; see this Dict. Letter.
     2. There is, on the part of the hirer, an implied obligation, not only
to use the thing with due care and moderation but not to apply it to any
other use than that for which it is hired; for example, if a horse is hired
as a saddle, horse; the hirer has no right to use the horse in a cart, or to
carry loads, or as a beast of burden. Pothier Louage, n. 189; Domat, B. 1,
tit. 4, Sec. 2, art. 2, 3; Jones' Bailm. 68, 88; 2 Saund. 47 g, and note; 1
Bell's Com. 454; 1 Cowen's R. 322; 1 Meigs, R. 459. If a carriage and horses
are hired to go from Philadelphia to New York, the hirer has no right to go
with them on a journey to Boston. Jones' Bailm. 68; 2 Ld. Raym. 915. So, if
they are hired for a week, he has no right to use them for a month, Jones'
Bailm. 68; 2 Ld. Raym. 915; 5 Mass. 104. And if the thing be used for a
different purpose from that which was intended by the parties, or in a
different manner, or for a longer period, the hirer is not only responsible
for all damages, but if a loss occur, although by inevitable casualty, he
will be responsible therefor. 1 Rep. Const. C. So. Car. 121; Jones' Bailm.
68, 121; 2 Ld. Raym. 909, 917. In short, such a misuser is deemed a
conversion of the property, for which the hirer is deemed responsible. Bac.
Abr. Bailment, C; Id. Trover, C, D, E; 2 Saund. 47 g; 2 Bulst. 306, 309.
     3. The above rules apply to cases where the hirer has the possession as
well as the use of the thing hired when the owner or his agents retain the
possession, the hirer is not in general responsible for an injury done to
it. For example, when the letter of a carriage and a pair of horses sent his
driver with them and an injury occurred, the hirer was held not to be
responsible. 9 Watts, R. 556, 562; 5 Esp. R. 263; Poth. Louage n. 196;
Jones, Bailm. 88; Story., Bailm. Sec. 403. But see 1 Bos. & P. 404, 409; 5
Esp. N. P. c 35; 10 Am. Jur. 256.
     4. Another implied obligation of the hirer is to restore the thing
hired, when the bailment, is determined. 4 T. R. 260; 3 Camp. 5, n.; 13
Johns. R. 211.
     5. The time, the place, and the mode of restitution of the thing hired,
are governed by the circumstances of each case depend and depend upon rules
of presumption of the intention of the parties, like those in other cases of
bailment. Story on Bailm.  Sec. 415
     6. There is also an implied obligation on the part of the hirer, to pay
the hire or recompense. Pothier, Louage, n. 134; Domat, B. 2, tit. 2, Sec.
2, n. 11 Code Civ; art. 1728.
     See, generally, Bouv. Inst. Index, h.t.; Employer; Letter.