ruminate

from The American Heritage® Dictionary of the English Language, 5th Edition.

• intransitive verb To turn a matter over and over in the mind.
• intransitive verb To chew cud.
• intransitive verb To reflect on over and over again.

from The Century Dictionary.

• To chew the cud, as a ruminant; practise rumination.
• To muse; meditate; think again and again; ponder: as, to ruminate on misfortunes.
• To chew again.
• To turn over in the mind; muse on; meditate over and over.
• In botany, appearing as if chewed: noting a structure of the endosperm (albumen) of a seed which gives a mottled appearance to its section, and which results from the infolding of a dark inner layer of the seed-coat into the lighter-colored matter of the endosperm, as in the nutmeg.

from the GNU version of the Collaborative International Dictionary of English.

• intransitive verb To chew the cud; to chew again what has been slightly chewed and swallowed.
• intransitive verb To think again and again; to muse; to meditate; to ponder; to reflect.
• transitive verb To chew over again.
• transitive verb To meditate or ponder over; to muse on.
• adjective (Bot.) Having a hard albumen penetrated by irregular channels filled with softer matter, as the nutmeg and the seeds of the North American papaw.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• verb intransitive To chew cud. (Said of ruminants.) Involves regurgitating partially digested food from the rumen.
• verb intransitive To meditate or reflect.
• adjective botany Having a hard albumen penetrated by irregular channels filled with softer matter, as the nutmeg and the seeds of the North American papaw.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• verb chew the cuds
• verb reflect deeply on a subject