This book suggests:
SALARY, salaire, F. From salarium, L. a stated
allowance of provisions given to a soldier, of which (sal)
salt was a necessary part; and hence the term came to signify pay or salary.
This other book suggests:
SALARY. Of or belonging to salt. Money given
to the soldiers for salt. (L. salarium.) (A. L.) [Andrew's Latin Lexicon]
Salt was held in great veneration by the ancients. It was always
used in sacrifices; thus also Moses ordained, —
"With all thine offerings thou shalt offer salt." Lev.ii.13.
Thus, to set salt before a stranger was, and still is, by
some Eastern nations reckoned a symbol of friendship; and
to spill the salt at table was esteemed ominous.
The desire to obtain means for the purchase of salt
gave rise to the word salarium, salary.
(A. R. A., p. 312.) [Adam's Roman Antiquities]
This book states:
Whenever a word loses a definite denotation, its meaning
is obviously generalized or diffused. Because people think
with varying degrees of definiteness, we find an almost inexhaustible
number of examples of generalization or blurring of meaning. For example,
salary comes from the Latin salarium, 'salt money,' part of pay of the
Roman soldiers. Ignorance and the lack of literacy have contributed their full share to linguistic change. Many of the words we use today
retain the fossils of the past; we can see in them forgotten uses and
customs.
This book has an interesting entry too. When listing words with the same origin but that are apparently so different (p.305), the following list about words derived from sal is included:
- Sauce (L. salsus, Fr. sauce), saucer (Sp. salsera, Fr. sauciere) and
sausage (Sp. salchicha, Fr. saucisse), salsify and salad (Sp. salado, salted), and saline and salary (L. salarium, lit. salt-money given to
the soldiers, or a stipend) are all derived from L. sal, salt (Sk, sara-s,
Gr. &Ag); as well as insular (= in sale).
On this same issue, this book states:
- sal, salis, salt; stem, sal-, sali-
Related words: saline, salad, sauce, sausage, saltpeter, salary, saucer, saucy.
Salary is from salarium, 'salt money paid a soldier.' A
saucer was a receptacle for sauce from salsus, 'salty,' which
is derived from sal. A saucy person is one whose talk is 'salted,'
sharp, or pert. Sausage comes through Late Latin salsicia from
Latin salsus, 'salty.'
(so sausage comes from sal too! Who would have thought that!)