What is "to be at home on any subject"

Home \Home\ (h[=o]m; 110), n. [OE. hom, ham, AS. h[=a]m; akin to OS. h[=e]m, D. & G. heim, Sw. hem, Dan. hiem, Icel. heimr abode, world, heima home, Goth. haims village, Lith. k["e]mas, and perh. to Gr. kw`mh village, or to E. hind a peasant; cf. Skr. ksh[=e]ma abode, place of rest, security, kshi to dwell. [root]20, 220.]

1. One's own dwelling place; the house in which one lives; esp., the house in which one lives with his family; the habitual abode of one's family; also, one's birthplace.

   The disciples went away again to their own home.
   --John xx. 10.

   Home is the sacred refuge of our life.
   --Dryden.

   Home! home! sweet, sweet home! There's no place like home.
   --Payne.

2. One's native land; the place or country in which one dwells; the place where one's ancestors dwell or dwelt. ``Our old home [England].''
   --Hawthorne.

3. The abiding place of the affections, especially of the domestic affections.

   He entered in his house -- his home no more, For without hearts there is no home.
   --Byron.

4. The locality where a thing is usually found, or was first found, or where it is naturally abundant; habitat; seat; as, the home of the pine.

   Her eyes are homes of silent prayer.
   --Tennyson.

   Flandria, by plenty made the home of war.
   --Prior.

5. A place of refuge and rest; an asylum; as, a home for outcasts; a home for the blind; hence, esp., the grave; the final rest; also, the native and eternal dwelling place of the soul.

   Man goeth to his long home, and the mourners go about the streets.
   --Eccl. xii. 5.

6. (Baseball) The home base; as, he started for home. At home.

   1. At one's own house, or lodgings.

   2. In one's own town or country; as, peace abroad and at home.

   3. Prepared to receive callers.

      Home department, the department of executive administration, by which the internal affairs of a country are managed. [Eng.]

      To be at home on any subject, to be conversant or familiar with it.

      To feel at home, to be at one's ease.

      To make one's self at home, to conduct one's self with as much freedom as if at home.

      Syn: Tenement; house; dwelling; abode; domicile.