sr.

(noun) a soft silver-white or yellowish metallic element of the alkali metal group; turns yellow in air; occurs in celestite and strontianite. Synonyms: strontium, Sr, atomic number 38.

(noun) the unit of solid angle adopted under the Systeme International d'Unites. Synonyms: steradian, sr.

(adj) used of the older of two persons of the same name especially used to distinguish a father from his son. Synonyms: elder, older. Example: "Bill adams, sr.."