Connotation (The positive or negative feeling of a word)

The connotation of a word is what kind of feeling it gives the reader/listener, in addition to its definition. This is not specific to English, and it is a hard thing for non-native speakers to get right – especially if they do not read a lot of well-written English!

I think the concept will be clear if I provide some examples.

Example: Grow

Grow has a neutral connotation. It can be used for good things and for bad things.

The tumor is growing. That is sad.
The economy is growing. That is great!

If we look up the verb grow in a thesaurus, we see many interesting synonyms:

Entry for "grow" in Thesaurus — *Entry for “grow” in the Oxford American Writer’s Thesaurus (included in the MacOS Dictionary app)*.

Here are some more synonyms, found on Thesaurus.com.

advance (positive connotation)

These predictions will advance our understanding of the mechanisms of…
Digital technologies in design, engineering and manufacture continue to advance.
Science can advance even without coherent models or unified theories.

expand (neutral connotation)

Deforestation is expanding into the Amazon region. (negative)
The charity’s outreach efforts are expanding (positive)

escalate (negative connotation)

If that party wins the election, the corruption which is already rampant will escalate to an unimaginable proportion

worsen (negative connotation)

enlarge (positive or neutral connotation)

Leaders should enlarge the circle of stakeholders.
Fresh thinking about interdependence can perhaps enlarge our political perspective.
Coupled B/Ba doping has been proved to enlarge the lattice parameters.

augment (positive connotation)

One of the most significant challenges is to integrate and augment sustainable urban forms with advanced technologies.

If you are still confused, let me know in the comments!