A line of iambic pentameter (our stock in trade) has a feminine ending when there are one or more unaccented syllables after the fifth stress. There are many feminine endings in Hamlet's speech:
To be, or not to be: that is the ques-tion:
Whether 'tis nobler in the mind to suf-fer
The slings and arrows of outrageous for-tune,
Or to take arms against a sea of trou-bles,
And by opposing, end them.
Our assumption is that Shakespeare can write regular iambic pentameter any time he wants to, and when he varies from it, he has a purpose. If the verse represents the character's thoughts, we assume that any turbulence in the verse represents some idea that causes the character distress for some reason. If a line ends with a feminine ending, we can pick out the exact word that is causing the character (Hamlet in this case) distress.
Question: Hamlet has questions about lots of things, but at the moment he's considering suicide. That question--"Should I end my life?"--causes Hamlet particular distress, and the end of the line goes awry.
Hamlet has so many feminine endings in this section that we might guess that he is troubled by some powerful idea, maybe an unconscious one. If you want to know what it is, please consider Hamlet's words
Suffer: Hamlet is suffering, and thinking about his pain deranges his thoughts, and the end of the line.
Fortune: thinking about the bad luck that destined Hamlet to set the disjointed time aright causes Hamlet distress, and muddles the end of the line.
Troubles: Hamlet feels that he has plenty.
End them: this isn't the end of the line, but the sentence ends on an unstressed syllable. Hamlet flinches at the idea of suicide implicit in the words.
No traveler returns
which appear later in this speech.
Sometimes people suggest that feminine endings are accidental because Shakespeare couldn't think of suitable monosyllables. I doubt that Shakespeare would have found conventional endings much of a challenge:
To be, or not to be: that is the point:
Whether 'tis nobler in the mind to bear
The slings and arrows of outrageous luck,
Or to take arms against a sea of woes,
And thereby end them all.
"Ugh! That's revolting!" Yep. But the point is that Shakespeare, if he'd wanted to, could have written lines with stessed endings.