Si op. sit, si opus sit, if it be necessary.
Si vir. perm., si vires permittant, if the strength allow it.
Signat., signatura, a label.
Sign. n. pr., signetur nomine proprio, let it be written upon, let it be signed with the proper name (not the trade name).
Sing., singulorum, of each.
S. S. S., stratum super stratum, layer upon layer.
Ss., semi, a half.
St., stet, let it stand; stent, let them stand.
Sub fin. coct., sub finem coctionis, towards the end of boiling, when the boiling is nearly finished.
Sum. tal., sumat talem, let the patient take one such as this.