The release of iOS8 introduced a third option to have text spoken called Speak Screen. This Speak Screen option now gives users the ability to have word definitions spoken out aloud!
The slideshow below describes the sequence. Please note that the Speak Screen feature must not be running when initially selecting a word.
Speak Screen can be switched on by going to Settings>General>Accessibility>Speech.
The reading experience can be also be personalised by selecting your preferred voice, its speaking rate and the highlighting of words as they are spoken.