A synonym for mastery might be:

Two that immediately come to mind are virtuosity and dexterity.

A synonym for mastery might be proficiency or comprehension.

Explanation:

Mastery means to have "comprehensive knowledge or skill in a subject or accomplishment. " (Source: Oxford).

Proficiency means to have "a high degree of competence or skill; expertise. " (Source: Oxford).

Comprehension means to have "the action or capability of understanding something. ".

Comprehension may be more mental focused than the connotation of mastery, but it still fits.

identify the subordinate clause in each of the following sentences. tell whether each clause is used as an adjective, an adverb, or a noun.

11.) emily dickinson, who was born in 1830in amherst, massachusetts, was a great american poet.

12.) she appeared to lead a fairly normal life until she became a recluse in her family's home.

13.) there she wrote poems that literary critics now call "great american poetry".

14.) unfortunately, only a few of dickinson's poems were published while she was alive.

15.) after she died in 1886, her other poems were published.

16.) i think everyone should reaad at least some of dickonson's poetry.

17.) dickinson is a poet whose work i now read often.

18.) the poems i have just finished reading are "a narrow fellow in the grass" and "apparently with no surprise"

19.) the rythyms of dickonson's poems are best appreciated when you read the poems aloud.

20.) whatever i read by emily dickonson surprises amd inspires me.